1. Field of the Invention
The present invention relates to a soil characteristics survey device and a soil characteristics survey method for surveying characteristics of a given soil, and more specifically, to a soil characteristics survey device which is used to collect information about the special distribution of soil characteristics within an agricultural field.
2. Description of the Background Art
In recent years, in an attempt to preserve the environment and improve profitability, precision agriculture has become a popular way to minimize the amount of investment required to purchase agricultural material, fertilizer, and feed to be consumed per unit area of the agriculture field.
In the precision agriculture, a comparatively large-scaled agricultural field is divided into plural sections, and these sections are individually managed with regard to fertilization or spraying agricultural chemicals, while taking different soil characteristics in the respective sections (variations in soil characteristics) into consideration.
In performing such precision agriculture, it is necessary to obtain information that accurately reflects the variations in the soil characteristics from section to section.
For example, the device disclosed in U.S. Pat. No. 5,044,756 is towed by a vehicle or the like and moves through the soil approximately horizontally at a predetermined depth. As it advances, the device projects light with a fixed wavelength into the soil and detects the reflected light, thereby surveying organic materials and water contained in the soil in real time qualitatively and quantitatively, based on characteristics of the reflected light.
The information corresponding to the respective sections is used to find the appropriate method for managing the soil characteristics in the individual section (including determination of the amount of fertilizer or agricultural chemicals to be given) by being compared with data information accumulated in the past or data information about other agricultural fields geographically different. Therefore, it is preferable that the data information corresponding to the respective sections is standardized (has a unified standard) so that it can be compared with data information about soil characteristics obtained from regions different in time and geography. In order to standardize the data information, plural parameters (variables) reflecting physical and chemical features of the soil can be adopted and expressed mathematically (as functions) so as to be used as indicators to evaluate the soil characteristics. When soil characteristics are evaluated in terms of superiority in agricultural production, essential parameters to define the soil characteristics include the clay content in the soil, the soil concentration, and so on, besides the amount of organic material or water (water content) contained in the soil to be surveyed by the above-mentioned device.
The parameters such as the clay content or the soil concentration are greatly affected by physical features of the soil (such as hardness or electric conductivity), and also it is difficult to find the quantity by an optical analyzing method. Consequently, it becomes necessary to use sensors having the function of detecting hardness and electric conductivity of the soil.
However, in the case where sensors having different detection principles are adopted to detect plural parameters at the same time, these sensors may detect various characteristics about the soil at sites apart from each other because of restrictions in installing positions and other reasons. For this, it cannot be certain that the various characteristics detected belong to the same sample.
In order to find the distribution of soil characteristics in an agricultural field, if parameters reflecting soil features are directly measured (detected) in the field, as in the above-mentioned device, it is likely that the relation between a detecting element and a sample (soil) has external perturbations. For example, in the case where detection is done by making the detecting element get in contact with the soil, it is likely that the contact pressure between the detecting element and the soil fluctuates, whereas in the case where detection is done by making the detecting element get out of contact with the soil, it is likely that the distance between the detecting element and the soil fluctuates. These external perturbations cause a decrease in the precision or reproducibility of obtained data.